Vias for cobalt-based interconnects and methods of fabrication thereof

ABSTRACT

Interconnect structures and corresponding techniques for forming the interconnect structures are disclosed herein. An exemplary interconnect structure includes a conductive feature that includes cobalt and a via disposed over the conductive feature. The via includes a first via barrier layer disposed over the conductive feature, a second via barrier layer disposed over the first via barrier layer, and a via bulk layer disposed over the second via barrier layer. The first via barrier layer includes titanium, and the second via barrier layer includes titanium and nitrogen. The via bulk layer can include tungsten and/or cobalt. A capping layer may be disposed over the conductive feature, where the via extends through the capping layer to contact the conductive feature. In some implementations, the capping layer includes cobalt and silicon.

This is a continuation application of U.S. patent application Ser. No.16/720,853, filed Dec. 19, 2019, which is a continuation application ofU.S. patent application Ser. No. 15/692,212, filed Aug. 31, 2017, nowU.S. Pat. No. 10,553,481, the entire disclosures of which areincorporated herein by reference.

BACKGROUND

The integrated circuit (IC) industry has experienced exponential growth.Technological advances in IC materials and design have producedgenerations of ICs, where each generation has smaller and more complexcircuits than the previous generation. In the course of IC evolution,functional density (i.e., the number of interconnected devices per chiparea) has generally increased while geometry size (i.e., the smallestcomponent (or line) that can be created using a fabrication process) hasdecreased. This scaling down process generally provides benefits byincreasing production efficiency and lowering associated costs.

Such scaling down has also increased the complexity of processing andmanufacturing ICs and, for these advances to be realized, similardevelopments in IC processing and manufacturing are needed. For example,copper-based interconnect structures typically implemented in multilayerinterconnect (MLI) features have presented performance, yield, and costchallenges as MLI features become more compact with ever-shrinking ICfeature size. For example, copper interconnects exhibit increasedresistance, poor electromigration performance, and voids duringfabrication as IC technologies expand into sub-20 nm technology nodes.Accordingly, although existing interconnect structures have beengenerally adequate for their intended purposes, they have not beenentirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a fragmentary diagrammatic view of an integrated circuitdevice, in portion or entirety, according to various aspects of thepresent disclosure.

FIG. 2A is an enlarged fragmentary diagrammatic view of the integratedcircuit device of FIG. 1 when implementing an interconnect structure, inportion or entirety, according to various aspects of the presentdisclosure.

FIG. 2B is an enlarged fragmentary diagrammatic view of the integratedcircuit device of FIG. 1 when implementing another interconnectstructure, in portion or entirety, according to various aspects of thepresent disclosure.

FIG. 2C is an enlarged fragmentary diagrammatic view of the integratedcircuit device of FIG. 1 when implementing yet another interconnectstructure, in portion or entirety, according to various aspects of thepresent disclosure.

FIG. 3 is a flow chart of a method for fabricating an interconnectstructure, such as the interconnect structures depicted in FIG. 1 and/orFIGS. 2A-2C, according to various aspects of the present disclosure.

FIG. 4 is a flow chart of a method for fabricating a via of aninterconnect structure, such as the interconnect structures depicted inFIG. 1 and/or FIGS. 2A-2C, according to various aspects of the presentdisclosure.

FIGS. 5A-5F are fragmentary diagrammatic views of an interconnectstructure, in portion or entirety, at various fabrication stages (suchas those associated with the method of FIG. 3 and/or FIG. 4) accordingto various aspects of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates generally to integrated circuit devices,and more particularly, to interconnect structures for integrated circuitdevices.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features.

IC manufacturing process flow is typically divided into threecategories: front-end-of-line (FEOL), middle-end-of-line (MEOL), andback-end-of-line (BEOL). FEOL generally encompasses processes related tofabricating IC devices, such as transistors. For example, FEOL processescan include forming isolation features, gate structures, and source anddrain features (generally referred to as source/drain features). MEOLgenerally encompasses processes related to fabricating contacts toconductive features (or conductive regions) of the IC devices, such ascontacts to the gate structures and/or the source/drain features. BEOLgenerally encompasses processes related to fabricating interconnectstructures that interconnect IC features fabricated by FEOL process(referred to herein as FEOL features or structures) and MEOL processes(referred to herein as MEOL features or structures), thereby enablingoperation of the IC devices. For example, BEOL processes can includeforming multilayer interconnect features that facilitate operation ofthe IC devices. As integrated circuit (IC) technologies progress towardssmaller technology nodes, BEOL processes have been observed to damageMEOL features and/or FEOL features. The present disclosure exploresimproved interconnect structures for protecting MEOL features and/orFEOL features from damage arising from BEOL processes.

FIG. 1 is a fragmentary diagrammatic view of an integrated circuitdevice 10, in portion or entirety, according to various aspects of thepresent disclosure. Integrated circuit device 10 may be included in amicroprocessor, a memory, and/or other integrated circuit device. Insome implementations, integrated circuit device 10 is a portion of anintegrated circuit (IC) chip, a system on chip (SoC), or portionthereof, that includes various passive and active microelectronicdevices such as resistors, capacitors, inductors, diodes, p-type fieldeffect transistors (PFETs), n-type field effect transistors (NFETs),metal-oxide semiconductor field effect transistors (MOSFETs),complementary metal-oxide semiconductor (CMOS) transistors, bipolarjunction transistors (BJTs), laterally diffused MOS (LDMOS) transistors,high voltage transistors, high frequency transistors, other suitablecomponents, or combinations thereof. The transistors may be planartransistors or multi-gate transistors, such as fin-like FETs (FinFETs).FIG. 1 has been simplified for the sake of clarity to better understandthe inventive concepts of the present disclosure. Additional featurescan be added in integrated circuit device 10, and some of the featuresdescribed below can be replaced, modified, or eliminated in otherembodiments of integrated circuit device 10.

Integrated circuit device 10 includes a substrate (wafer) 12. In thedepicted embodiment, substrate 12 includes silicon. Alternatively oradditionally, substrate 12 includes another elementary semiconductor,such as germanium; a compound semiconductor, such as silicon carbide,gallium arsenide, gallium phosphide, indium phosphide, indium arsenide,and/or indium antimonide; an alloy semiconductor, such as silicongermanium (SiGe), GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP;or combinations thereof. Alternatively, substrate 12 is asemiconductor-on-insulator substrate, such as a silicon-on-insulator(SOI) substrate, a silicon germanium-on-insulator (SGOI) substrate, or agermanium-on-insulator (GOI) substrate. Semiconductor-on-insulatorsubstrates can be fabricated using separation by implantation of oxygen(SIMOX), wafer bonding, and/or other suitable methods. Substrate 12 caninclude various doped regions (not shown) depending on designrequirements of integrated circuit device 10. In some implementations,substrate 12 includes p-type doped regions (for example, p-type wells)doped with p-type dopants, such as boron (for example, BF₂), indium,other p-type dopant, or combinations thereof. In some implementations,substrate 12 includes n-type doped regions (for example, n-type wells)doped with n-type dopants, such as phosphorus, arsenic, other n-typedopant, or combinations thereof. In some implementations, substrate 12includes doped regions formed with a combination of p-type dopants andn-type dopants. The various doped regions can be formed directly onand/or in substrate 12, for example, providing a p-well structure, ann-well structure, a dual-well structure, a raised structure, orcombinations thereof. An ion implantation process, a diffusion process,and/or other suitable doping process can be performed to form thevarious doped regions.

An isolation feature(s) (not shown) is formed over and/or in substrate12 to isolate various regions, such as various device regions, ofintegrated circuit device 10. For example, isolation features define andelectrically isolate active device regions and/or passive device regionsfrom each other. Isolation features include silicon oxide, siliconnitride, silicon oxynitride, other suitable isolation material, orcombinations thereof. Isolation features can include differentstructures, such as shallow trench isolation (STI) structures, deeptrench isolation (DTI) structures, and/or local oxidation of silicon(LOCOS) structures. In some implementations, isolation features includeSTI features. For example, STI features can be formed by etching atrench in substrate 12 (for example, by using a dry etch process and/orwet etch process) and filling the trench with insulator material (forexample, by using a chemical vapor deposition process or a spin-on glassprocess). A chemical mechanical polishing (CMP) process may be performedto remove excessive insulator material and/or planarize a top surface ofisolation features. In some embodiments, STI features include amulti-layer structure that fills the trenches, such as a silicon nitridelayer disposed over an oxide liner layer.

Various gate structures are disposed over substrate 12, such as a gatestructure 20A, a gate structure 20B, and a gate structure 20C. In someimplementations, one or more of gate structures 20A-20C interpose asource region and a drain region, where a channel region is definedbetween the source region and the drain region. The one or more gatestructures 20A-20C engage the channel region, such that current can flowbetween the source/drain regions during operation. In someimplementations, gate structures 20A-20C are formed over a finstructure, such that gate structures 20A-20C each wrap a portion of thefin structure. For example, one or more of gate structures 20A-20C wrapchannel regions of the fin structure, thereby interposing a sourceregion and a drain region of the fin structure. Gate structures 20A-20Cinclude metal gate (MG) stacks, such as metal gate stack 22A, metal gatestack 22B, and metal gate stack 22C. Metal gate stacks 22A-22C areconfigured to achieve desired functionality according to designrequirements of integrated circuit device 10, such that metal gatestacks 22A-22C include the same or different layers and/or materials. Insome implementations, metal gate stacks 22A-22C include a gatedielectric (for example, a gate dielectric layer) and a gate electrode(for example, a work function layer and a bulk conductive layer). Metalgate stacks 22A-22C may include numerous other layers, for example,capping layers, interface layers, diffusion layers, barrier layers, hardmask layers, or combinations thereof. In some implementations, the gatedielectric layer is disposed over an interfacial layer (including adielectric material, such as silicon oxide), and the gate electrode isdisposed over the gate dielectric layer. The gate dielectric layerincludes a dielectric material, such as silicon oxide, high-k dielectricmaterial, other suitable dielectric material, or combinations thereof.Examples of high-k dielectric material include hafnium dioxide (HfO₂),HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconium oxide, aluminum oxide,hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, other suitable high-kdielectric materials, or combinations thereof. In some implementations,the gate dielectric layer is a high-k dielectric layer. The gateelectrode includes a conductive material, such as polysilicon, aluminum(Al), copper (Cu), titanium (Ti), tantalum (Ta), tungsten (W),molybdenum (Mo), cobalt (Co), TaN, NiSi, CoSi, TiN, WN, TiAl, TiAlN,TaCN, TaC, TaSiN, other conductive material, or combinations thereof. Insome implementations, the work function layer is a conductive layertuned to have a desired work function (such as an n-type work functionor a p-type work function), and the conductive bulk layer is aconductive layer formed over the work function layer. In someimplementations, the work function layer includes n-type work functionmaterials, such as Ti, silver (Ag), TaAl, TaAlC, TiAlN, TaC, TaCN,TaSiN, manganese (Mn), zirconium (Zr), other suitable n-type workfunction materials, or combinations thereof. In some implementations,the work function layer includes a p-type work function material, suchas TiN, TaN, ruthenium (Ru), Mo, Al, WN, ZrSi₂, MoSi₂, TaSi₂, NiSi₂, WN,other suitable p-type work function materials, or combinations thereof.The bulk (or fill) conductive layer includes a suitable conductivematerial, such as Al, W, and/or Cu. The bulk conductive layer mayadditionally or collectively include polysilicon, Ti, Ta, metal alloys,other suitable materials, or combinations thereof.

Gate structures 20A-20C are formed by deposition processes, lithographyprocesses, etching processes, other suitable processes, or combinationsthereof. The deposition processes include CVD, physical vapor deposition(PVD), atomic layer deposition (ALD), high density plasma CVD (HDPCVD),metal organic CVD (MOCVD), remote plasma CVD (RPCVD), plasma enhancedCVD (PECVD), low-pressure CVD (LPCVD), atomic layer CVD (ALCVD),atmospheric pressure CVD (APCVD), plating, other suitable methods, orcombinations thereof. The lithography patterning processes includeresist coating (for example, spin-on coating), soft baking, maskaligning, exposure, post-exposure baking, developing the resist,rinsing, drying (for example, hard baking), other suitable processes, orcombinations thereof. Alternatively, the lithography exposure process isassisted, implemented, or replaced by other methods, such as masklesslithography, electron-beam writing, or ion-beam writing. The etchingprocesses include dry etching processes, wet etching processes, otheretching processes, or combinations thereof. Metal gate stacks 22A-22Care fabricated according to a gate last process, a gate first process,or a hybrid gate last/gate first process. In gate last processimplementations, gate structures 20A-20D include dummy gate stacks thatare subsequently replaced with metal gate stacks 22A-22C. The dummy gatestacks include, for example, an interfacial layer (including, forexample, silicon oxide) and a dummy gate electrode layer (including, forexample, polysilicon). In such implementations, the dummy gate electrodelayer is removed, thereby forming openings (trenches) in which metalgate stacks 22A-22C are formed.

Gate structures 20A-20C further include spacers 26A-26C, which aredisposed adjacent to (for example, along sidewalls of) metal gate stacks22A-22C, respectively. Spacers 26A-26C are formed by any suitableprocess and include a dielectric material. The dielectric material caninclude silicon, oxygen, carbon, nitrogen, other suitable material, orcombinations thereof (for example, silicon oxide, silicon nitride,silicon oxynitride, or silicon carbide). For example, in the depictedembodiment, a dielectric layer including silicon and nitrogen, such as asilicon nitride layer, can be deposited over substrate 12 andsubsequently anisotropically etched to form spacers 26A-26C. In someimplementations, spacers 26A-26C include a multi-layer structure, suchas a first dielectric layer that includes silicon nitride and a seconddielectric layer that includes silicon oxide. In some implementations,more than one set of spacers, such as seal spacers, offset spacers,sacrificial spacers, dummy spacers, and/or main spacers, are formedadjacent to metal gate stacks 22A-22C. In such implementations, thevarious sets of spacers can include materials having different etchrates. For example, a first dielectric layer including silicon andoxygen (for example, silicon oxide) can be deposited over substrate 12and subsequently anisotropically etched to form a first spacer setadjacent to metal gate stacks 22A-22C (or dummy metal gate stacks, insome implementations), and a second dielectric layer including siliconand nitrogen (for example, silicon nitride) can be deposited oversubstrate 12 and subsequently anisotropically etched to form a secondspacer set adjacent to the first spacer set. Implantation, diffusion,and/or annealing processes may be performed to form lightly doped sourceand drain (LDD) features and/or heavily doped source and drain (HDD)features in substrate 12 before and/or after forming spacers 26A-26C,depending on design requirements of integrated circuit device 10.

Epitaxial source features and epitaxial drain features (referred to asepitaxial source/drain features) are disposed in source/drain regions ofsubstrate 12. For example, a semiconductor material is epitaxially grownon substrate 12, forming epitaxial source/drain features 30 over asource region and a drain region of substrate 12. In the depictedembodiment, gate structure 20B interposes epitaxial source/drainfeatures 30, and a channel region is defined between epitaxialsource/drain features 30. Gate structure 20B and epitaxial source/drainfeatures 30 thus form a portion of a transistor, such a pull-uptransistor or a pull-down transistor, of integrated circuit device 10.Gate structure 20B and/or epitaxial source/drain features 30 are thusalternatively referred to as device features. In some implementations,epitaxial source/drain features 30 wrap source/drain regions of a finstructure. An epitaxy process can implement CVD deposition techniques(for example, vapor-phase epitaxy (VPE), ultra-high vacuum CVD(UHV-CVD), LPCVD, and/or PECVD), molecular beam epitaxy, other suitableSEG processes, or combinations thereof. The epitaxy process can usegaseous and/or liquid precursors, which interact with the composition ofsubstrate 12. Epitaxial source/drain features 30 are doped with n-typedopants and/or p-type dopants. In some implementations, where integratedcircuit device 10 is configured as an n-type device (for example, havingan n-channel), epitaxial source/drain features 30 are epitaxial layersincluding silicon and/or carbon, where silicon-containing epitaxiallayers or silicon-carbon-containing epitaxial layers are doped withphosphorous, other n-type dopant, or combinations thereof (for example,forming a Si:P epitaxial layer or a Si:C:P epitaxial layer). In someimplementations, where integrated circuit device 10 is configured as ap-type device (for example, having a p-channel), epitaxial source/drainfeatures 30 are epitaxial layers including silicon and germanium, wherethe silicon germanium containing epitaxial layers are doped with boron,other p-type dopant, or combinations thereof (for example, forming aSi:Ge:B epitaxial layer). In some implementations, epitaxialsource/drain features 30 include materials and/or dopants that achievedesired tensile stress and/or compressive stress in the channel region.In some implementations, epitaxial source/drain features 30 are dopedduring deposition by adding impurities to a source material of theepitaxy process. In some implementations, epitaxial source/drainfeatures 30 are doped by an ion implantation process subsequent to adeposition process. In some implementations, annealing processes areperformed to activate dopants in epitaxial source/drain features 30and/or other source/drain regions of integrated circuit device 10 (forexample, HDD regions and/or LDD regions).

A multilayer interconnect (MLI) feature 40 is disposed over substrate12. MLI feature 40 electrically couples various devices (for example,transistors, resistors, capacitors, and/or inductors) and/or components(for example, gate structures and/or source/drain features) ofintegrated circuit device 10, such that the various devices and/orcomponents can operate as specified by design requirements of integratedcircuit device 10. MLI feature 40 includes a combination of dielectriclayers and conductive layers configured to form various interconnectstructures. The conductive layers are configured to form verticalinterconnect features, such as device-level contacts and/or vias, and/orhorizontal interconnect features, such as conductive lines. Verticalinterconnect features typically connect horizontal interconnect featuresin different layers (or different planes) of MLI feature 40. In someimplementations, vertical interconnect features and horizontalinterconnect features have respective lengths and widths measured alongthe same direction, where vertical interconnect features have lengthsgreater than their widths, and horizontal interconnect features havelengths less their widths. During operation of integrated circuit device10, the interconnect structures are configured to route signals betweenthe devices and/or the components of integrated circuit device 10 and/ordistribute signals (for example, clock signals, voltage signals, and/orground signals) to the devices and/or the components of integratedcircuit device 10. It is noted that though MLI feature 40 is depictedwith a given number of dielectric layers and conductive layers, thepresent disclosure contemplates MLI feature 40 having more or lessdielectric layers and/or conductive layers depending on designrequirements of integrated circuit device 10.

In FIG. 1, MLI feature 40 includes one or more dielectric layers, suchas an interlayer dielectric layer 42 (ILD-0) disposed over substrate 12,an interlayer dielectric layer 44 (ILD-1) disposed over ILD layer 42, aninterlayer dielectric layer 46 (ILD-2) disposed over ILD layer 44, andan interlayer dielectric layer 48 (ILD-3) disposed over ILD layer 46.ILD layers 42-48 include a dielectric material including, for example,silicon oxide, silicon nitride, silicon oxynitride, TEOS formed oxide,PSG, BPSG, low-k dielectric material, other suitable dielectricmaterial, or combinations thereof. Exemplary low-k dielectric materialsinclude FSG, carbon doped silicon oxide, Black Diamond® (AppliedMaterials of Santa Clara, Calif.), Xerogel, Aerogel, amorphousfluorinated carbon, Parylene, BCB, SILK (Dow Chemical, Midland, Mich.),polyimide, other low-k dielectric material, or combinations thereof. Inthe depicted embodiment, ILD layers 42-48 are dielectric layers thatinclude a low-k dielectric material (generally referred to as low-kdielectric layers). ILD layers 42-48 can include a multilayer structurehaving multiple dielectric materials. MLI feature 40 can further includeone or more contact etch stop layers (CESL) disposed over substrate 12,such as a CESL 52 disposed between ILD layer 42 and ILD layer 44, a CESL54 disposed between ILD layer 44 and ILD layer 46, and a CESL 56disposed between ILD layer 46 and ILD layer 48. In some implementations,a CESL (not shown) is also disposed between substrate 12 and ILD layer42. CESLs 52-56 include a material different than ILD layers 42-48, suchas a dielectric material that is different than the dielectric materialof ILD layers 42-48. In the depicted embodiment, where ILD layers 42-48include a low-k dielectric material, CESLs 52-56 include silicon andnitrogen (for example, silicon nitride or silicon oxynitride). ILDlayers 42-48 and/or CESLs 52-56 are formed over substrate 12, forexample, by a deposition process (such as CVD, PVD, ALD, HDPCVD, MOCVD,RPCVD, PECVD, LPCVD, ALCVD, APCVD, plating, other suitable methods, orcombinations thereof). In some implementations, ILD layers 42-48 and/orCESLs 52-56 are formed by a flowable CVD (FCVD) process that includes,for example, depositing a flowable material (such as a liquid compound)over substrate 12 and converting the flowable material to a solidmaterial by a suitable technique, such as thermal annealing and/orultraviolet radiation treating. Subsequent to the deposition of ILDlayers 42-48 and/or CESLs 52-56, a CMP process and/or otherplanarization process is performed, such that ILD layers 42-48 and/orCESLs 52-56 have substantially planar surfaces.

A device-level contact 60, a device-level contact 62, a device-levelcontact 64, a via 70, a via 72, a via 74, a conductive line 80, aconductive line 82, and a conductive line 84 are disposed in ILD layers42-48 to form interconnect structures. Device-level contacts 60-64 (alsoreferred to as local interconnects or local contacts) electricallycouple and/or physically couple IC device features to other conductivefeatures of MLI feature 40. For example, device-level contact 60 is ametal-to-poly (MP) contact, which generally refers to a contact to agate structure, such as a poly gate structure or a metal gate structure.In the depicted embodiment, device-level contact 60 is disposed on gatestructure 20B (in particular, metal gate stack 22B), such thatdevice-level contact 60 connects gate structure 20B to via 70.Device-level contact 60 extends through ILD layer 44 and CESL 52, thoughthe present disclosure contemplates embodiments where device-levelcontact 60 extends through more than one ILD layer and/or CESL of MLIfeature 40. In furtherance of the example, device-level contact 62 anddevice-level contact 64 are metal-to-device (MD) contacts, whichgenerally refer to contacts to a conductive region of integrated circuitdevice 10, such as source/drain regions. In the depicted embodiment,device-level contact 62 and device-level contact 64 are disposed onrespective epitaxial source/drain features 30, such that device-levelcontact 62 and device-level contact 64 connect epitaxial source/drainfeatures 30 respectively to via 72 and via 74. Device-level contact 62and device-level contact 64 extend through ILD layer 42, ILD layer 44,and CESL 52, though the present disclosure contemplates embodimentswhere device-level contact 62 and/or device-level contact 64 extendthrough more than one ILD layer and/or CESL of MLI feature 40. In someimplementations, device-level contacts 60-64 are MEOL conductivefeatures that interconnect FEOL conductive features (for example, gatestructures 20A-20C and/or epitaxial source/drain features 30) to BEOLconductive features (for example, vias 70-74), thereby electricallyand/or physically coupling FEOL conductive features to BEOL conductivefeatures.

Vias 70-74 electrically couple and/or physically couple conductivefeatures of MLI feature 40 to one another. For example, via 70 isdisposed on device-level contact 60, such that via 70 connectsdevice-level contact 60 to conductive line 80; via 72 is disposed ondevice-level contact 62, such that via 72 connects device-level contact62 to conductive line 82; and via 74 is disposed on device-level contact64, such that via 74 connects device-level contact 64 to conductive line84. In the depicted embodiment, vias 70-74 extend through ILD layer 46and CESL 54, though the present disclosure contemplates embodimentswhere vias 70-74 extend through more than one ILD layer and/or CESL ofMLI feature 40. In some implementations, vias 70-74 are BEOL conductivefeatures that interconnect MEOL conductive features (for example,device-level contacts 60-64) to BEOL conductive features (for example,conductive lines 80-84), thereby electrically and/or physically couplingMEOL conductive features to BEOL conductive features. In someimplementations, MLI feature 40 further includes vias that are BEOLconductive features that interconnect BEOL conductive features indifferent ILD layers to one another, such as conductive lines 80-84 toconductive lines (not shown) disposed in other ILD layers (not shown)overlying ILD layers 42-48, thereby electrically and/or physicallycoupling BEOL conductive features of integrated circuit device 10.

Device-level contacts 60-64, vias 70-74, and conductive lines 80-84include any suitable conductive material, such as Ta, Ti, Al, Cu, Co,tantalum nitride (TaN), titanium (Ti), titanium nitride (TiN), cobalt(Co), and/or other suitable conductive materials. Device-level contacts60-64, vias 70-74, and conductive lines 80-84 are formed by patterningILD layers 42-48 and/or CESLs 52-56. Patterning ILD layers 42-48 andCESLs 52-56 can include lithography processes and/or etching processesto form openings (trenches), such as contact openings and/or lineopenings in respective ILD layers 42-48 and/or CESLs 52-56. In someimplementations, the lithography processes include forming a resistlayer over respective ILD layers 42-48 and/or CESLs 52-56, exposing theresist layer to pattern radiation, and developing the exposed resistlayer, thereby forming a patterned resist layer that can be used as amasking element for etching opening(s) in respective ILD layers 42-48and/or CESLs 52-56. The etching processes include dry etching processes,wet etching processes, other etching processes, or combinations thereof.Thereafter, the opening(s) are filled with one or more conductivematerials. The conductive material(s) can be deposited by PVD, CVD, ALD,electroplating, electroless plating, other suitable deposition process,or combinations thereof. Thereafter, any excess conductive material(s)can be removed by a planarization process, such as a CMP process,thereby planarizing a top surface of ILD layers 42-48, CESLs 52-56,device-level contacts 60-64, vias 70-74, and/or conductive lines 80-84.

Interconnect structures of MLI features, such as MLI feature 40,typically include copper. As IC technologies progress towards smallertechnology nodes (such as 16 nm, 10 nm, 7 nm, 5 nm, and below) and MLIfeatures become more compact, copper-based interconnect structures havebeen observed to degrade performance, develop voids (arising, forexample, from higher aspect ratio interconnect openings), and increaseresistance-capacitance (RC) delay in ICs. To compensate for theseissues, IC manufacturers are exploring new materials for theinterconnect structures, such as aluminum, tungsten, cobalt, and/orruthenium. For example, cobalt and/or tungsten may be implemented indevice-level contacts, such as device-level contacts 60-64, whilealuminum and/or tungsten may be implemented in vias, such as vias 70-74.Cobalt, in particular, exhibits better sheet resistance and/orelectromigration (EM) performance than traditional interconnectmaterials, such as copper, and is easily integrated into conventional ICfabrication processes. A via disposed on a device-level contact thusoften includes a tungsten barrier layer disposed along sidewall surfacesand/or bottom surfaces of a via opening (defined, for example, by an ILDlayer and/or the device-level contact) and a tungsten bulk layerdisposed over the tungsten barrier layer, where the tungsten barrierlayer and the tungsten bulk layer fill the via opening.

Though the tungsten bulk layer exhibits desirable sheet resistance andthe tungsten barrier layer exhibits desirably low contact resistance,poor adhesion of the tungsten barrier layer to the sidewall surfacesand/or bottom surfaces of the via opening leads to significant damage ofthe device-level contact, particularly when the device-level contactincludes cobalt. For example, BEOL processing associated withtungsten-containing vias (from, for example, depositing the tungstenbulk layer, planarizing the tungsten barrier layer and/or the tungstenbulk layer, and/or cleaning processes) and/or associated with conductivelines (for example, cleaning processes) of the interconnect structurehave been observed to seep through gaps between the tungsten barrierlayer and the ILD layer and attack material of the device-level contact(in particular, cobalt), degrading its performance. Such performancedegradation is calamitous for cobalt-containing device-level contacts.For example, cobalt loss arising from exposure to chemicals during BEOLprocessing, such as CMP slurry (which is typically an acidic solvent),have been observed to cause significant yield loss of cobalt-containingdevice-level contacts, which is unacceptable for meeting shrinkingtechnology node demands.

The present disclosure thus proposes vias that protect device-levelcontacts (and, in some implementations, conductive lines), particularlycobalt-containing device-level contacts, from post-process damage. Inparticular, vias disclosed in FIGS. 2A-2C below, which can beimplemented in vias 70-74, include a multi-layer via barrier thatadheres well to sidewall surfaces and/or bottom surfaces of a viaopening (defined, for example, by an ILD layer and/or the device-levelcontact), eliminating (or significantly reducing) any loss of materialof device-level contacts during BEOL processing. In particularimplementations, the multi-layer via barrier includes a titanium layerand a titanium nitride layer, generally referred to as a Ti/TiN viabarrier, which has been observed to enable low resistance while adheringsufficiently to the surfaces defining the via opening, therebypreventing damage to underlying conductive features. In someimplementations, no changes in device performance were observed afterBEOL processing. For example, comparing dark voltage contrast (DVC)images generated from e-beam inspection of surface charge after a CMPprocess of a conventional via having a tungsten barrier and a via havinga Ti/TiN via barrier as described herein, it has been observed that thevia having the Ti/TiN via barrier is voltage-contrast type defect free(indicating that no voids (resulting, for example, from cobalt lossduring the CMP process) are present in the via and/or device-levelcontact), while the conventional via having the tungsten barrier hasvoltage-contrast type defects (indicating that voids, which can causeelectrical shorts or opens, are present in the via and/or device-levelcontact). In another example, it has been observed that a via having theTi/TiN contact barrier described herein can significantly reduceresistance (in some implementations, as much as 77%) between the via andother IC features. For example, in some implementations, the via havingthe Ti/TiN contact barrier is physically coupled to an FEOL feature,such as a via physically coupled to a resistor of integrated circuitdevice 10, where an interface between the via and the FEOL feature hasbeen observed to exhibit reduced resistance. Different embodiments mayhave different advantages, and no particular advantage is required ofany embodiment.

FIG. 2A is an enlarged fragmentary diagrammatic view of a portion A ofintegrated circuit device 10 when implementing an interconnect structure100A, in portion or entirety, according to various aspects of thepresent disclosure. Interconnect structure 100A includes device-levelcontact 62, via 72, and conductive line 82, where via 72 extends throughILD layer 46 and CESL 54 to interconnect device-level contact 62 toconductive line 82. FIG. 2A has been simplified for the sake of clarityto better understand the inventive concepts of the present disclosure.Additional features can be added in interconnect structure 100A, andsome of the features described below can be replaced, modified, oreliminated in other embodiments of interconnect structure 100A.

In FIG. 2A, device-level contact 62 includes cobalt (and is thusreferred to as a cobalt-containing device-level contact). In someimplementations, a volume of device-level contact 62 includes at least65% cobalt. For example, device-level contact 62 includes acobalt-containing bulk layer 102, which includes cobalt or a cobaltalloy (for example, including titanium, tungsten, nickel, phosphorous,boron, aluminum, tantalum, other suitable cobalt alloying material, orcombinations thereof). In some implementations, cobalt-containing bulklayer 102 includes at least 50% cobalt. Device-level contact 62 furtherincludes a capping layer 104 disposed on cobalt-containing bulk layer102. In the depicted embodiment, capping layer 104 includes cobalt andsilicon (for example, cobalt silicide). Though not depicted, in someimplementations, device-level contact 62 includes a barrier layer and/oradhesion layer, where cobalt-containing bulk layer 102 is disposed overthe barrier layer and/or adhesion layer. In some implementation,device-level contact 62 extends through an opening in one or more ILDlayers and/or ESL layers. For example, cobalt-containing bulk layer 102fills an opening defined by sidewalls of ILD layer 44 and/or CESL 52 anda bottom defined by metal gate stack 22B. In implementations wheredevice-level contact 62 includes a barrier layer and/or other suitabledevice-level contact layer, the barrier layer and/or other suitabledevice-level contact layer conform to the opening, such that the barrierlayer and/or other suitable device-level contact layer are disposed onthe dielectric layer and the metal gate stack 22B and cobalt-containingbulk layer 102 is disposed on the barrier layer and/or other suitabledevice-level contact layer.

Via 72 fills a via opening having sidewalls defined by ILD layer 46,CESL 54, and capping layer 104 and a bottom defined by cobalt-containingbulk layer 102. Via 72 includes a multi-layer via barrier 110, such as afirst via barrier layer 112 and a second via barrier layer 114. Firstvia barrier layer 112 and second via barrier layer 114 are configured tofacilitate adhesion of via 72 to surfaces defining the via opening, suchas the sidewall surfaces defined by ILD layer 46, CESL 54, and cappinglayer 104 and bottom surface(s) defined by cobalt-containing bulk layer102. First via barrier layer 112 is disposed on the sidewalls and thebottom of the via opening, such that first via barrier layer 112 isdisposed on ILD layer 46, CESL 54, cobalt-containing bulk layer 102,capping layer 104. Second via barrier layer 114 is disposed on first viabarrier layer 112, such that second via barrier layer 114 extends alongthe sidewalls and the bottom of the via opening defined by ILD layer 46,CESL 54, cobalt-containing bulk layer 102, capping layer 104. In thedepicted embodiment, first via barrier layer 112 and second via barrierlayer 114 have substantially uniform thicknesses. In someimplementations, first via barrier layer 112 has a thickness of about 20Å to about 90 Å, and second via barrier layer 114 has a thickness ofabout 1 Å to about 40 Å. In some implementations, a thickness of firstvia barrier layer 112 is greater than a thickness of second via barrierlayer 114.

First via barrier layer 112 includes titanium (and is alternativelyreferred to as a titanium-containing barrier layer or a titanium barrierlayer), and second via barrier layer 114 includes titanium and nitrogen(and is alternatively referred to as a titanium-and-nitrogen-containingbarrier layer or a titanium nitride barrier layer). Titanium exhibitslow resistance while adhering well to dielectric materials, such as ILDlayer 46 and/or CESL 54, eliminating (or minimizing) any gaps formedbetween via 72 and ILD layer 46 and/or CESL 54. First via barrier layer112 and second via barrier layer 114 thus prevent chemicals fromattacking and/or consuming device-level contact 62 during subsequentprocessing, such as described herein. In some implementations, first viabarrier layer 112 includes at least 90% titanium, and second via barrierlayer 114 includes at least 90% combined of titanium and nitrogen. Insome implementations, second via barrier layer 114 includes at least 35%titanium and at least 35% nitrogen. In some implementations, first viabarrier layer 112 and second via barrier layer 114 are formed usingdeposition processes configured to provide high bottom coverage (HBC),which further enhances adhesion of multi-layer via barrier 110. Forexample, first via barrier layer 112 is formed by a PVD process or anALD process, and second via barrier layer 114 is formed by a CVD processor a plasma-based or gas-based treatment process.

Via 72 further includes a via bulk (fill) layer 120 disposed overmulti-layer via barrier 110. Via bulk layer 120 includes tungsten or atungsten alloy (and is alternatively referred to as atungsten-containing via bulk layer or a via bulk tungsten layer). In thedepicted embodiment, via bulk layer 120 includes a tungsten-containingseed (or liner) layer 122 and a tungsten-containing bulk layer 124.Tungsten-containing seed layer 122 is disposed on second via barrierlayer 114, such that tungsten-containing seed layer 122 extends alongthe sidewalls and the bottom of the via opening defined by ILD layer 46,CESL 54, cobalt-containing bulk layer 102, and capping layer 104.Tungsten-containing bulk layer 124 is disposed on tungsten-containingseed layer 122. In some implementations, tungsten-containing seed layer122 has a thickness of about 1 Å to about 40 Å, and tungsten-containingbulk layer 124 has a thickness of about 100 nm to about 200 nm. In someimplementations, tungsten-containing seed layer 122 is formed using anALD process, and tungsten-containing bulk layer 124 is formed using aCVD process.

Conductive line 82 is disposed over via 72, for example, on multi-layervia barrier 110 and via bulk layer 120. Conductive line 82 includescopper or a copper alloy (and is alternatively referred to as acopper-containing line or a copper line). In the depicted embodiment,conductive line 82 includes a barrier layer 132 and a copper-containingbulk layer 134. Barrier layer 132 is disposed on multi-layer via barrier110 and via bulk layer 120, and copper-containing bulk layer 134 isdisposed on barrier layer 132. Barrier layer 132 includes titanium,tantalum, other suitable material, or combinations thereof. For example,barrier layer 132 includes TiN or TaN. In some implementations, barrierlayer 132 is omitted from conductive line 82. Alternatively oradditionally, conductive line 82 can include other conductive materials,such as tantalum, tantalum nitride, titanium, titanium nitride,aluminum, tungsten, polysilicon, cobalt, other suitable conductivematerials, or combinations thereof.

FIG. 2B is an enlarged fragmentary diagrammatic view of portion A ofintegrated circuit device 10 when implementing an interconnect structure100B, in portion or entirety, according to various aspects of thepresent disclosure. Interconnect structure 100B is similar tointerconnect structure 100A, except capping layer 104 is omitted fromdevice-level contact 62 in interconnect structure 100B. Via 72 thusfills a via opening having sidewalls defined by ILD layer 46 and CESL 54and a bottom defined by cobalt-containing bulk layer 102, wheremulti-layer via barrier 110 enhances adhesion of via 72 to ILD layer 46and/or CESL 54 while exhibiting low resistance. FIG. 2B has beensimplified for the sake of clarity to better understand the inventiveconcepts of the present disclosure. Additional features can be added ininterconnect structure 100B, and some of the features described belowcan be replaced, modified, or eliminated in other embodiments ofinterconnect structure 100B.

FIG. 2C is an enlarged fragmentary diagrammatic view of portion A ofintegrated circuit device 10 when implementing an interconnect structure100C, in portion or entirety, according to various aspects of thepresent disclosure. Interconnect structure 100C is similar tointerconnect structure 100A, except capping layer 104 is omitted fromdevice-level contact 62 in interconnect structure 100C. Via 72 thusfills a via opening having sidewalls defined by ILD layer 46 and CESL 54and a bottom defined by cobalt-containing bulk layer 102, wheremulti-layer via barrier 110 enhances adhesion of via 72 to ILD layer 46and/or CESL 54 while exhibiting low resistance. Further, in contrast tointerconnect structure 100A, via bulk layer 120 includes acobalt-containing bulk layer 126 in interconnect structure 100C.Cobalt-containing bulk layer 126 includes cobalt or a cobalt alloy. Insome implementations, cobalt-containing bulk layer 126 includes at least50% cobalt. In some implementations, via bulk layer 120 further includesa cobalt-containing seed layer configured similar to tungsten-containingseed layer 122 of interconnect structure 100A. In some implementations,conductive line 82 includes cobalt or a cobalt alloy, instead of copperor a copper alloy. FIG. 2C has been simplified for the sake of clarityto better understand the inventive concepts of the present disclosure.Additional features can be added in interconnect structure 100C, andsome of the features described below can be replaced, modified, oreliminated in other embodiments of interconnect structure 100C.

FIG. 3 is a flow chart of a method 200 for fabricating an interconnectstructure, such as interconnect structures 100A-100C in FIGS. 2A-2C,according to various aspects of the present disclosure. At block 210,method 200 includes forming a device-level contact over a substrate. Atblock 220, a via is formed on the device-level contact. At block 230, aconductive line is formed on the via. At block 240, the method 200 maycontinue to complete fabrication of the interconnect structure.Additional steps can be provided before, during, and after method 200,and some of the steps described can be moved, replaced, or eliminatedfor additional embodiments of method 200.

FIG. 4 is a flow chart of a method 250 for fabricating a via of aninterconnect structure, such as via 72 of interconnect structures100A-100C in FIGS. 2A-2C, according to various aspects of the presentdisclosure. In some implementations, method 250 can be implemented inmethod 200 at block 220. At block 252, method 250 includes forming anopening in a dielectric layer overlying a conductive structure thatincludes cobalt. At block 254, a first via barrier layer that includesincludes titanium is formed on sidewall surfaces and a bottom surface ofthe opening. At block 256, a second via barrier layer that includestitanium and nitrogen is formed on the first via barrier layer. Atblock, a via bulk layer is formed on the second via barrier layer, suchthat the first via layer, the second via layer, and the via fill layerfill the opening. Additional steps can be provided before, during, andafter method 250, and some of the steps described can be moved,replaced, or eliminated for additional embodiments of method 250.

FIGS. 5A-5F are fragmentary diagrammatic views of an interconnectstructure 300, in portion or entirety, at various fabrication stages(such as those associated with method 200 of FIG. 3 and/or method 250 ofFIG. 4) according to various aspects of the present disclosure.Interconnect structure 300 includes a via that protects underlyingconductive features, such as underlying MEOL features and/or BEOLfeatures, from damage during subsequent processing, as described herein.FIGS. 5A-5F have been simplified for the sake of clarity to betterunderstand the inventive concepts of the present disclosure. Additionalfeatures can be added in interconnect structure 300, and some of thefeatures described below can be replaced, modified, or eliminated inother embodiments of interconnect structure 300.

In FIG. 5A, a substrate 310 is provided having a conductive feature 320disposed thereover. Substrate 310 is similar to substrate 12 depictedand described in FIG. 1. In the depicted embodiment, conductive feature320 is a MEOL feature, such as a cobalt-containing device-level contactsimilar to device-level contact 62 depicted and described in FIG. 1 andFIGS. 2A-2C. For example, conductive feature 320 includes acobalt-containing contact layer 322, similar to cobalt-containing bulklayer 102, and a capping layer 324, similar to capping layer 104.Alternatively, in some implementations, conductive feature 320 is acobalt-containing BEOL feature, such as a cobalt-containing conductiveline of MLI feature 40. In some implementations, cobalt-containingcontact layer 322 is formed by any suitable deposition process (forexample, PVD, CVD, ALD, or other suitable deposition process) and/orannealing process. In some implementations, the deposition process usesa cobalt precursor, such as cyclopentadienyl cobalt dicarbonyl(CpCo(CO)₂), dicobalt hexcarbonyl tertbutylacctylene (CCTBA), cobalttricarbonyl nitrosyl (Co(CO)₃NO), bis(cyclopentadienyl)cobalt(Co(C₅H₅)₂, CpCo(CO)₂), bis(ethylcyclopentadienyl)cobalt (C₁₄H₁₈Co),bis(pentamethylcyclopentadienyl)cobalt (C₂₀H₃₀Co), cobalttris(2,2,6,6-tetramethyl-3,5-heptanedionate)(Co(OCC(CH₃)₃CHCOC(CH₃)₃)₃), bis(ethylcyclopentadienyl)cobalt(C₁₄H₁₈Co), other suitable cobalt precursor, or combinations thereof.

A dielectric layer 330, similar to ILD layers 42-48 depicted anddescribed in FIG. 1 and FIGS. 2A-2C, is formed over conductive feature320. For example, a CVD process is performed to deposit a low-kdielectric material over conductive feature 320, thereby formingdielectric layer 330. A CESL 332, similar to CESLs 52-56 depicted anddescribed in FIG. 1 and FIGS. 2A-2C, can be formed over dielectric layer330 before forming dielectric layer 330, though the present disclosurecontemplates embodiments where CESL 332 is omitted from interconnectstructure 300. CESL 332 includes a material having a different etchingcharacteristic than a material of dielectric layer 330, such as siliconnitride.

In FIG. 5B, a via opening 340 is formed in dielectric layer 330 (and, insome implementations, CESL 332) by a patterning process. In the depictedembodiment, via opening 340 extends vertically through dielectric layer330, CESL 332, and capping layer 324. Via opening 340 includes asidewall 334 (defined by dielectric layer 330, CESL 332, and cappinglayer 324), a sidewall 336 (defined by dielectric layer 330, CESL 332,and capping layer 324), and a bottom 338 (defined by cobalt-containingcontact layer 322) that extends between sidewall 334 and sidewall 336.The patterning process includes lithography processes and/or etchingprocesses. For example, forming via opening 340 includes performing alithography process to form a patterned resist layer over dielectriclayer 330 and performing an etching process to transfer a patterndefined in the patterned resist layer to dielectric layer 330. Thelithography process can include forming a resist layer on dielectriclayer 330 (for example, by spin coating), performing a pre-exposurebaking process, performing an exposure process using a mask, performinga post-exposure baking process, and performing a developing process.During the exposure process, the resist layer is exposed to radiationenergy (such as ultraviolet (UV) light, deep UV (DUV) light, or extremeUV (EUV) light), where the mask blocks, transmits, and/or reflectsradiation to the resist layer depending on a mask pattern of the maskand/or mask type (for example, binary mask, phase shift mask, or EUVmask), such that an image is projected onto the resist layer thatcorresponds with the mask pattern. Since the resist layer is sensitiveto radiation energy, exposed portions of the resist layer chemicallychange, and exposed (or non-exposed) portions of the resist layer aredissolved during the developing process depending on characteristics ofthe resist layer and characteristics of a developing solution used inthe developing process. After development, the patterned resist layerincludes a resist pattern that corresponds with the mask. The etchingprocess uses the patterned resist layer as an etch mask to removeportions of dielectric layer 330. The etching process can include a dryetching process (for example, a reactive ion etching (RIE) process), awet etching process, other suitable etching process, or combinationsthereof. After the etching process, the patterned resist layer isremoved from dielectric layer 330, for example, by a resist strippingprocess. In some implementations, the patterned resist layer is used asan etch mask to remove portions of CESL 332 and/or capping layer 324 toextend via opening 340, thereby exposing conductive feature 320. In someimplementations, dielectric layer 330 and/or CESL 332 are used asetching masks to remove portions respectively of CESL 332 and/or cappinglayer 324. Various selective etching processes can be performed.Alternatively, the exposure process can be implemented or replaced byother methods, such as maskless lithography, electron-beam (e-beam)writing, ion-beam writing, and/or nanoimprint technology.

In FIG. 5C, a via barrier layer 350 is formed in via opening 340. Viabarrier layer 350 is similar to first via barrier layer 112 depicted anddescribed in FIGS. 2A-2C. For example, via barrier layer 350 is atitanium-containing layer. Via barrier layer 350 is disposed alongsidewall 334, sidewall 336, and bottom 338 defining via opening 340,such that via barrier layer 350 partially fills via opening 340. In thedepicted embodiment, via barrier layer 350 is disposed directly onportions of dielectric layer 330, CESL 332, and cobalt-containingcontact layer 322 that define via opening 340. In furtherance of thedepicted embodiment, a PVD process conformally deposits via barrierlayer 350, such that via barrier layer 350 has a thickness that issubstantially uniform over exposed surfaces of interconnect structure300. Alternatively, via barrier layer 350 is formed by CVD, ALD,electroplating, electroless plating, other suitable deposition process,or combinations thereof.

In FIG. 5D, a via barrier layer 352 is formed in via opening 340. Viabarrier layer 352 is similar to second via barrier layer 114 depictedand described in FIGS. 2A-2C. For example, via barrier layer 352 is atitanium-and-nitrogent-containing layer. Via barrier layer 352 is formedover via barrier layer 350, such that via barrier layer 352 partiallyfills via opening 340. In the depicted embodiment, via barrier layer 352is disposed directly on via barrier layer 350. In furtherance of thedepicted embodiment, a CVD process conformally deposits via barrierlayer 352, such that via barrier layer 352 has a thickness that issubstantially uniform over exposed surfaces of interconnect structure300. Alternatively, via barrier layer 352 is formed by PVD, ALD,electroplating, electroless plating, other suitable deposition process,or combinations thereof.

In FIG. 5E, a via bulk layer 354 is formed in via opening 340. Via bulklayer 354 is similar to via bulk layer 120 depicted and described inFIGS. 2A-2C. In the depicted embodiment, via bulk layer 354 is atungsten-containing layer. For example, via bulk layer 354 includes aseed layer 356, such as tungsten-containing seed layer 122 depicted anddescribed in FIG. 2A and FIG. 2B, and a fill layer 358, such astungsten-containing bulk layer 124 depicted and described in FIG. 2A andFIG. 2B. Alternatively, via bulk layer 120 is a cobalt-containing layer,such as cobalt-containing bulk layer 126 depicted and described in FIG.2C. Via bulk layer 354 is formed over via barrier layer 352, such thatvia bulk layer 354 fills any remaining via opening 340. In the depictedembodiment, seed layer 356 is disposed directly on via barrier layer352, and fill layer 358 is disposed directly on seed layer 356. Infurtherance of the depicted embodiment, an ALD process conformallydeposits seed layer 356, such that seed layer 356 has a thickness thatis substantially uniform over exposed surfaces of interconnect structure300, and a CVD process deposits fill layer 358 over exposed surfaces ofinterconnect structure 300. Alternatively, via bulk layer 354, seedlayer 356 and/or fill layer 358 are formed by PVD, CVD, ALD,electroplating, electroless plating, other suitable deposition process,or combinations thereof.

In FIG. 5F, a CMP process and/or other planarization process isperformed on interconnect structure 300. The CMP process removesexcessive via barrier layer 350, via barrier layer 352, and via bulklayer 354, resulting in a via 360 that includes via barrier layer 350,via barrier layer 352, and via bulk layer 354 (which fill via opening340). The CMP process planarizes a top surface of interconnect structure300, such that in some implementations, a top surface of dielectriclayer 330 and a top surface of via 360 form a substantially planarsurface. Thereafter, fabrication of interconnect structure 300 cancontinue with forming a conductive feature over via 360, where via 360physically and/or electrically couples the conductive feature toconductive feature 320. For example, the conductive feature is a BEOLfeature, such as conductive line 82 depicted and described in FIGS.2A-2C. The conductive feature can be formed in a dielectric layerdisposed over via 360 by implementing the deposition, lithography,and/or etching processes described herein.

The present disclosure provides for many different embodiments.Interconnect structures and corresponding techniques for forming theinterconnect structures are disclosed herein. An exemplary interconnectstructure includes a conductive feature that includes cobalt and a viadisposed over the conductive feature. The via includes a first viabarrier layer disposed over the conductive feature, a second via barrierlayer disposed over the first via barrier layer, and a via bulk layerdisposed over the second via barrier layer. The first via barrier layerincludes titanium, and the second via barrier layer includes titaniumand nitrogen. The via bulk layer can include tungsten and/or cobalt. Acapping layer may be disposed over the conductive feature, where the viaextends through the capping layer to contact the conductive feature. Insome implementations, the capping layer includes cobalt and silicon. Insome implementations, the conductive feature and the via are disposed ina dielectric layer. In some implementations, the conductive feature is amiddle-end-of-line conductive feature. In some implementations, theconductive feature is a back-end-of-line conductive feature.

Another exemplary interconnect structure includes a cobalt-containingdevice contact disposed over a substrate and a dielectric layer disposedover the cobalt-containing device contact. A via is disposed in thedielectric layer. The via includes a titanium-containing barrier layerdisposed over sidewall surfaces defined by the dielectric layer and abottom surface defined by the cobalt-containing device contact, atitanium-and-nitrogen-containing barrier layer disposed over thetitanium-containing barrier layer, and a bulk layer disposed over thetitanium-and-nitrogen-containing barrier layer. In some implementations,the cobalt-containing device contact includes a cobalt-containingcontact layer and a cobalt-and-silicon-containing capping layer disposedon the cobalt-containing contact layer. In such implementations, the viaextends through the cobalt-and-silicon-containing capping layer to thecobalt-containing contact layer. In some implementations, theinterconnect structure further includes a copper-containing conductiveline, wherein the via interconnects the cobalt-containing device contactto the copper-containing conductive line.

An exemplary method includes forming an opening in a dielectric layer,wherein the opening overlies a conductive feature that includes cobalt.The method further includes forming a first via barrier layer oversidewalls and a bottom defining the opening, forming a second viabarrier layer over the first via barrier layer, and forming a via bulklayer over the second via barrier layer. The first via barrier layerincludes titanium, and the second via barrier layer includes titaniumand nitrogen. The first via barrier layer, the second via barrier layer,and the via bulk layer fill the opening. In some implementations, thefirst via barrier layer is formed by performing a physical vapordeposition process. In some implementations, the second via barrierlayer is formed by performing a chemical vapor deposition process. Insome implementations, the method further includes forming a cappinglayer over the conductive feature. In some implementations, the cappinglayer includes cobalt and silicon.

Another exemplary method includes forming a middle-end-of-line (MEOL)feature over a substrate, wherein the MEOL feature includes cobalt andforming a back-end-of-line (BEOL) feature on the MEOL feature. Formingthe BEOL feature includes forming a dielectric layer over the MEOLfeature, patterning the dielectric layer to form an opening in thedielectric layer, wherein the opening has sidewalls defined by thedielectric layer and a bottom defined by an exposed portion of the MEOLfeature, depositing a titanium-containing barrier layer on the sidewallsand the bottom of the opening, depositing atitanium-and-nitrogen-containing barrier layer on thetitanium-containing barrier layer, depositing a bulk layer on thetitanium-and-nitrogen-containing barrier layer, wherein thetitanium-containing barrier layer, the titanium-and-nitrogen-containingbarrier layer, and the bulk layer fill the opening, and performing aplanarizing process on the titanium-containing barrier layer, thetitanium-and-nitrogen-containing barrier layer, and the bulk layer,thereby planarizing a surface of the BEOL feature. In someimplementations, the depositing the titanium-containing barrier layerincludes performing a physical vapor deposition process. In someimplementations, the depositing the titanium-and-nitrogen-containingbarrier layer includes performing a chemical vapor deposition process.In some implementations, the forming the MEOL feature includes forming acobalt-containing contact layer and forming acobalt-and-silicon-containing contact layer over the cobalt-containingcontact layer. The cobalt-containing contact layer and thecobalt-and-silicon-containing contact layer are disposed in anotherdielectric layer.

An exemplary integrated circuit device includes a back-end-of-line(BEOL) feature configured to electrically couple a cobalt contactfeature to a conductive feature. The BEOL feature includes atitanium-containing barrier layer disposed on the cobalt contactfeature, a titanium-and-nitrogen-containing barrier layer disposed onthe titanium-containing barrier layer, and a bulk layer disposed on thetitanium-and-nitrogen-containing barrier layer. In some implementations,the BEOL feature is a first BEOL feature, the cobalt contact feature isa middle-end-of-line (MEOL) feature, and the conductive feature is asecond BEOL feature, such that the first BEOL feature electricallycouples the MEOL feature to the second BEOL feature. In someimplementations, the BEOL feature is a first BEOL feature, the cobaltcontact feature is a second BEOL feature, and the conductive feature isa third BEOL feature, such that the first BEOL feature electricallycouples the second BEOL feature to the third BEOL feature.

Another exemplary integrated circuit device includes a multilayerinterconnect (MLI) feature that includes a device contact, a via, and aconductive line. The device contact is configured to electrically couplean integrated circuit device feature to the via. The via is configuredto electrically couple the device contact to the conductive line. Thevia includes a first via barrier layer disposed on the device contact,wherein the device contact includes cobalt and the first via barrierlayer includes titanium, a second via barrier layer disposed on thefirst via barrier layer, wherein the second via barrier layer includestitanium and nitrogen, and a via bulk layer disposed on the second viabarrier layer. In some implementations, the device contact includes acontact layer that includes cobalt and a capping layer disposed on thecontact layer, wherein the capping layer includes cobalt and silicon. Insuch implementations, the via extends through the capping layer to thecontact layer. In some implementations, the integrated circuit devicefeature is a gate structure or a source/drain feature.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An interconnect structure comprising: a cobaltlayer disposed in a dielectric layer over a substrate, wherein thecobalt layer is electrically connected to a transistor at the substrate;a titanium layer, a titanium nitride layer, and a first metal layersequentially disposed over the cobalt layer and in the dielectric layer,wherein the titanium nitride layer wraps the first metal layer, thetitanium layer wraps the titanium nitride layer, and a width of aninterface between the titanium layer and the cobalt layer is less than awidth of the cobalt layer; and a second metal layer disposed in thedielectric layer, wherein an interface is between the second metal layerand the titanium layer, the titanium nitride layer, and the first metallayer.
 2. The interconnect structure of claim 1, wherein: the cobaltlayer includes at least 50% cobalt; the titanium layer includes at least90% titanium; and the titanium nitride layer includes at least 35%titanium and at least 35% nitrogen.
 3. The interconnect structure ofclaim 1, wherein a thickness of the titanium nitride layer is less thana thickness of the titanium layer.
 4. The interconnect structure ofclaim 1, wherein the cobalt layer is a first cobalt layer, the firstmetal layer is a second cobalt layer, and the second cobalt layerdirectly contacts the titanium nitride layer.
 5. The interconnectstructure of claim 1, wherein the first metal layer includes a tungstenlayer and a tungsten seed layer, wherein the tungsten seed layer isbetween the tungsten layer and the titanium nitride layer.
 6. Theinterconnect structure of claim 1, wherein the second metal layerincludes a copper layer.
 7. The interconnect structure of claim 1,wherein the cobalt layer is a first cobalt layer and the second metallayer is a second cobalt layer.
 8. The interconnect structure of claim1, wherein the first metal layer includes a first metal and the secondmetal layer includes a second metal that is different than the firstmetal.
 9. The interconnect structure of claim 1, further comprising acobalt silicide layer, wherein an interface is between the cobaltsilicide layer and the cobalt layer and an interface is between thecobalt silicide layer and the titanium layer.
 10. The interconnectstructure of claim 1, wherein the cobalt layer is electrically connectedto a gate of the transistor.
 11. The interconnect structure of claim 1,wherein the cobalt layer is electrically connected to a source of thetransistor.
 12. The interconnect structure of claim 1, wherein thecobalt layer is electrically connected to a drain of the transistor. 13.An interconnect structure comprising: a first contact having acobalt-containing bulk layer; a second contact that physically contactsthe first contact, wherein the second contact has a bilayer barrierlayer and a metal-containing bulk layer, the bilayer barrier layerincludes a titanium-containing layer and a titanium-and-nitrogencontaining layer, the metal-containing bulk layer includes a first metaldifferent than titanium, and the titanium-containing layer forms abottom surface of the second contact and physically contacts a topsurface of the cobalt-containing bulk layer of the first contact; and athird contact that physically contacts the second contact, wherein ametal-containing bulk layer of the third contact includes a second metaldifferent than the first metal and titanium.
 14. The interconnectstructure of claim 13, wherein the bilayer barrier layer of the secondcontact is U-shaped.
 15. The interconnect structure of claim 13, whereinthe first contact, the second contact, and the third contact aredisposed in a dielectric layer and the dielectric layer physicallycontacts the top surface of the cobalt-containing bulk layer of thefirst contact.
 16. The interconnect structure of claim 13, furthercomprising a cobalt silicide layer that physically contacts the topsurface of the cobalt-containing bulk layer.
 17. The interconnectstructure of claim 13, wherein the first metal is cobalt.
 18. Theinterconnect structure of claim 13, wherein the first metal is tungsten.19. A method of forming an interconnect structure, the methodcomprising: forming an opening in a dielectric layer that exposes acobalt-containing bulk layer of a first contact of the interconnectstructure; forming a bilayer barrier layer of a second contact of theinterconnect structure that partially fills the opening, wherein theforming the bilayer barrier layer includes: depositing a titanium layerto form a bottom of the second contact that physically contacts thecobalt-containing bulk layer and sidewalls of the second contact thatphysically contact the dielectric layer, and depositing a titaniumnitride layer over the titanium layer; depositing a metal-containingbulk layer of the second contact in the opening over the titaniumnitride layer, wherein the metal-containing bulk layer of the secondcontact includes a first metal different than titanium; removing themetal-containing bulk layer, the titanium nitride layer, and thetitanium layer of the second contact that is disposed over a top surfaceof the dielectric layer; and forming a third contact of the interconnectstructure that physically contacts the second contact, wherein ametal-containing bulk layer of the third contact includes a second metalthat is different than the first metal and titanium.
 20. The method ofclaim 19, further comprising forming the opening in a cobalt silicidelayer to expose the cobalt-containing bulk layer of the first contact.